Satellite Constellations Are Too Bright for Astronomy

Bright spacecraft spoil aesthetic appreciation of the night sky for amateur astronomers and interfere with professional research. But there are already several thousand spacecraft in orbit and that number is expected to grow to tens of thousands in the coming years: Industries and governments are launching six major “constellations” of communication satellites: Starlink, BlueBird, Qianfan, Guowang, OneWeb and Kuiper.

In response to this problem, the International Astronomical Union created a Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS). The IAU CPS recently recommended brightness limits for constellation satellites. Those limits are designed to ensure that satellites in operational orbits are never visible to the unaided eye. But I (Anthony Mallama) and my colleague Richard Cole have found that companies aren’t abiding by these limits.

In dark-sky locations, people can see objects of visual magnitude 6, which I refer to as the aesthetic limit. For professional astronomers, the research limit is magnitude 7 for satellites at altitudes up to 550 km and it gradually becomes fainter at higher elevations.

To study the brightness of large satellite constellations, Cole and I combine visual magnitude estimates made by amateur observers with data recorded electronically by professionals. We have already published results for Starlink, BlueBird, Qianfan, and OneWeb spacecraft. Research is currently underway on the Guowang and Kuiper constellations.

Except for two satellite types — OneWeb and Starlink Mini satellites at 485 km — all of the satellites are brighter than the aesthetic limit. And every satellite constellation except OneWeb exceeds the research limit.

The BlueBird satellites operated by AST SpaceMobile are the brightest of the bunch, but their number is far smaller than the constellations.

SpaceX’s Starlink V2 Mini satellites are about the same brightness as the (now discontinued) first-generation versions — even though the V2 Minis (despite their name) have more than four times the surface area. That accomplishment illustrates the success of the company’s brightness mitigation efforts.  

Meanwhile, the Chinese constellations, Qianfan and Guowang, are too bright even at their current high orbits around 1,000 km. (We have sufficient data to characterize Guowang brightness, so it is included here, but the results are not yet published.) Later launches will aim for orbits in the 300 to 500 km range, which would make the spacecraft 1 to 2 magnitudes brighter than they are now.

The Kuiper spacecraft from Amazon are the newest constellation. Amazon has applied brightness mitigation, and we are currently collecting data to assess its effectiveness.

These results and future findings will be published on a new website: satmags.netlify.app. Meanwhile, amateur observers are invited to participate by recording satellite magnitudes. This paper explains how.